WASHINGTON (Reuters) - Papayas have extra copies of genes
that make them sweet and nutritious, researchers reported on
Wednesday in a study that can help shed light on how flowering
plants evolved.

They published the complete genetic sequence of the "SunUp"
papaya, a tree genetically engineered to be virus resistant.

Writing in the journal Nature, they said the plant has
fewer genes than the more thoroughly studied weed Arabdopsis,
yet has a longer DNA sequence.

They believe they have pinpointed genes responsible for
helping tree-like plants evolve, and genes that helped make it
smell and taste so good, attracting animals and people to
spread its seeds.

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Papayas have extra genes that appear to code for these
aromas and for storing starch, presumably in the fruit.

"This also foreshadows what we might expect to discover in
the genomes of other fragrant-fruited trees, as well as plants
with striking fragrance of leaves (herbs), flowers or other
organs," Maqsudul Alam of the University of Hawaii and
colleagues wrote.

"Papaya is an exceptionally promising system for the
exploration of tropical-tree genomes and fruit-tree genomics,"
they added.

"Arguably, the sequencing of the genome of SunUp papaya
makes it the best-characterized commercial transgenic crop."

The fruit is commercially valuable.

"Papaya is ranked first on nutritional scores among 38
common fruits, based on the percentage of the United States
Recommended Daily Allowance for vitamin A, vitamin C,
potassium, folate, niacin, thiamine, riboflavin, iron and
calcium, plus fiber," they wrote.

"Consumption of its fruit is recommended for preventing
vitamin A deficiency, a cause of childhood blindness in
tropical and subtropical developing countries."